Broadseam is a term particular to the making of a sail

Sail

A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

. The panels that make up the sections of a sail are cut with curves on the connecting edges or seam

Seam

Seam may refer to:* Seam , the line where two or more layers of fabric are held together by stitches* Seam , a stratum of coal or mineral that is economically viable; a bed or a distinct layer of vein of rock in other layers of rock...

s. This method adds a three dimensional

Dimension

In physics and mathematics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it...

 shape to what would ordinarily be a flat triangular or rectangular piece of fabric. Since a sail is a type of airfoil

Airfoil

An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....

, this method of sail making adds significantly to the amount of draft

Draft (hull)

The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...

a sail can have.